A plastic scrap of a runner, a failed mold product or the like discharged from a molding machine is crushed, mixed with a virgin material and is recycled to a mold material of a plastic product.
In a field of plastic molding referred to as so-to-speak fine stable molding, by simply crushing a plastic scrap as described above, a crush material thereof is mixed with small powders or large or small nonuniform crush particles, and when the crush material is used for plastic molding as it is, there is a concern of hampering the fine stable molding of a plastic.
Therefore, when the fine stable molding of a plastic is carried out, there is needed a pellet forming apparatus pelletizing the temporarily crushed crush material to a constant size.
According to a pellet forming apparatus of pelletizing the crush material, generally, a melted plastic is passed through a die from extruding means of a hot rotation screw type to constitute a strand and is continuously extruded. The strand extruded by passing the die is successively cut uniformly to a constant length by a cutter to form into a pellet.
Meanwhile, the strand extruded from the die and brought into an uncooled molten state is provided with an adhering force, and when the strand is cut into a plurality of pellets by the cutter as it is, the plurality of pellets become large particles by sticking together or the like.
Therefore, a normal pellet forming apparatus is provided with a water tank stored with cooling water for cooling and solidifying the strand extruded from the die and brought into the molten state. Further, the strand extruded from the die is cooled to solidify by passing the strand through the water tank. Thereafter, the strand is successively and evenly cut to a constant length to form into a pellet by a cutter by reeling the cooled and solidified strand by a pinch roller or the like.
The generally-used pellet forming apparatus is provided with a large-sized extruding means of the hot rotation screw type, the large-sized water tank of the water cooling type for cooling the strand and the like, occupies a wide installing area and is expensive.
Therefore, the apparatus is unsuitable for being used at a plastic injection molding site having a narrow installing area.
Further, according to the normally-used water cooling type pellet forming apparatus, when a plastic scrap to be pelletized is switched to that of a different kind or a different color, there is needed a troublesome and laborious setting operation or the like of passing again the newly switched strand formed to be cooled of a different kind or a different color through the water tank stored with cooling water, and enormous time and labor are required for the switching. Further, also when a middle portion of the strand is temporarily interrupted to cut by some cause, there is needed the troublesome and laborious setting operation of passing again the strand through the water tank stored with cooling water.
Further, the normally-used pellet forming apparatus is of the water cooling type for passing the strand through the water tank stored with the cooling water to cool and solidify, and therefore, after cutting the cooled and solidified strand into a pellet, a post step of drying the pellet is needed, and the equipment is large-sized and also expensive by that amount.
Owing to the reason, the normally-used water cooling type pellet forming apparatus is unsuitable for being installed at a plastic molding site to be used.
As pellet forming apparatus for resolving the difficulties, there are apparatus described in JP-A-9-29739, JP-A-2001-88196, and JP-A-2002-59419 of an air cooling type of cooling and solidifying a strand extruded from a die and brought into a molten state by the atmosphere by excluding a large-sized water tank of cooling and solidifying a strand.
Among them, the apparatus described in JP-A-9-29739 is constituted by a structure of introducing to cool a strand extruded by passing a die from a hot rotation screw and brought into a molten state to an inner side of a bush/mechanical element of an air cooling type by being guided at inside of a groove for guiding.
Therefore, according to the apparatus, as described in paragraph 0002 of JP-A-9-193158, the strand brought into the uncooled molten state is guided in the guiding groove while staying in an uncooled soft state immediately after having been extruded from the die, in that occasion, a diameter of the strand guided at inside of the guiding groove does not become uniform but unstable.
Further, according to the apparatus, there is frequently brought about a situation in which a cooling efficiency in cooling the strand by blowing air to a surrounding of the strand brought into the molten state passing through the inner side of the bush/mechanical element is poor, and the strand is discharged to outside of the bush/mechanical element without being sufficiently cooled and solidified.
A cause thereof resides in that a large amount of air for cooling blown to the inner side of the bush/mechanical element is not circulated at a surrounding of the strand passing through the inner side of the bush/mechanical element but is leaked to outside of the bush/mechanical element from widely opened upper end opening portion or lower end opening portion of the bush/mechanical element. Further, the strand is cooled by using air in a normal temperature state, and therefore, when the atmospheric temperature is high, there is brought about a situation in which the strand is not sufficiently cooled and solidified.
Further, according to the apparatus, when the strand is going to be formed from a state of a low die temperature, a front end of the strand in an uncooled and soft state extruded from a strand forming path of the die and is bent in a ring-like shape. Further, the front end of the strand bent in the ring-like state closes the upper end opening portion of the bush/mechanical element without being smoothly introduced to the inner side of the bush/mechanical element by being passed through the groove for guiding. Further, the pellet forming apparatus cannot continuously be operated.
The apparatus described in JP-A-2001-88196 is constituted by a structure of cooling and solidifying a strand by blowing air from a blower to the strand extruded from the die and brought into the molten state. A metal net is expanded on a side opposed to the blower by interposing a path of the strand therebetween. Further, there is constituted a structure in which the strand is prevented from being bent considerably by receiving a wind pressure of air blown from the blower by the metal net.
According to the apparatus, a large amount of air for cooling blown from the blower is firmly brought into contact with the strand which is uncooled and brought into a soft state, is not circulated at a surrounding of the strand but is wastefully passed to a side of the metal net of a portion remote from the strand. Therefore, there is a difficulty that the strand is not efficiently and sufficiently cooled and solidified.
Therefore, according to the apparatus, the path for blowing air for cooling from the and blower passing the strand brought into the uncooled soft state is set to be long and the strand is continued to be cooled by a long distance and for a long time period. Therefore, the strand brought into the soft state is brought into a state of being prolongedly hung to a downward side of the die, and the strand disposed at a vicinity of the die is brought into a state of being elongated to be long by receiving a self weight of the strand which is prolongedly hung. Further, there is a difficulty of considerably varying an outer diameter of the strand extruded from the die.
Further, according to the apparatus, there is brought about a situation in which owing to a style of cooling the strand brought into the molten state by air in a normal temperature state, the strand is not sufficiently cooled and solidified by being influenced by a variation in the atmospheric temperature.
The apparatus of JP-A-2002-59419 is provided with a guide roller at a midway of a path of the strand to prolong a time period of cooling the strand brought into the molten state. Further, the strand extruded from the die and brought into the uncooled soft state is circulated to pass a surrounding of the guide roller substantially in a V-like shape by a long distance. Further, there is constituted a structure of sufficiently cooling and solidifying the strand by air by taking time.
According to the apparatus, in starting to operate the apparatus, there is needed a troublesome and laborious setting operation of making a strand extruded from the die and brought into the molten state wrap on the surrounding of the guide roller or the like. Further, the apparatus is large-sized by an amount of adding the guide roller and is unsuitable for an apparatus of being used by being placed at a plastic molding site an installing area of which is intended to be narrowed.